Ink jet inks must have a very low viscosity, typically less than about 20 centipoise at the jetting temperature. While hot melt inks have been used, liquid inks are generally more suited to high volume industrial printing. One way to achieve this low viscosity is by including a substantial amount of organic liquids. In general, ink containing a substantial amount of organic liquids would produce undesirable emissions during the printing process. Such emissions are substantially avoided, however, with energy curable inks. Energy curable inks use low viscosity reactive materials to attain the desired viscosity. The reactive materials have reactive groups that are cured after printing with radiation, such as UV radiation or electron beams.
The low viscosity reactive materials in energy curable inks may include low viscosity monomers and low viscosity oligomers. The energy curable inks may also include higher viscosity reactive and unreactive oligomers and polymers. Because monofunctional monomers are particularly low in viscosity, ink jet inks to date have included substantial amounts of monofunctional monomers. On the other hand, monofunctional monomers are in general the most volatile of the reactive materials that might be included, resulting in some evaporation and undesirable emissions during the printing process. It would, therefore, be desirable to omit or limit the most volatile monofunctional monomers.
It would also be desirable to formulate and ink jet ink that would print well onto plastic substrates.